Place the neonatal animals in a plastic bag and without squeezing them, squeeze all of the air out of the bag. Refill the bag slowly with CO2, doing it slowly ensures you do not freeze the animals. Repeat this step two more times to ensure the environment is 100% CO2. Once the bag is full of CO2, seal it and wait until the pups have been motionless and lose color for at least a half an hour. ( Sundberg, J. & Boggess, D, p. 68-69 ) It may be necessary to clip the spine with sharp scissors immediately after removing the animals from the bag to ensure death.
In this case, we are talking about having your pet put to sleep by a vet in the comfort of the home. For more on this read the hub " putting dog to sleep at home ". Also, you may want to think in advance about what to do if your pet dies at home. The article " what to do if dog dies at home " may be also helpful. If you decide to go this route, make sure you contact your vet in advance and arrange a plan should your pet suddenly deteriorate during your vet's office after hours. It's a good idea to have several emergency phone numbers to keep on hand should your vet for some reason not be available. There's nothing worse than watching your pet take a turn for the worse and not being able to find a vet to come to your home to allow your pet to rest in peace.